Abstract
Large Eddy Simulations of two-phase flames with the Conditional Moment Closure combustion model have been performed for flow conditions corresponding to stable and blow-off regimes in a swirl n-heptane spray burner. In the case of stable flame (i.e. low air velocity), the predicted mean and r.m.s. velocities and the location and shape of the flame agree reasonably well with experiment. In particular, the presence of localised extinctions is captured in agreement with experiment. Using model constants previously calibrated against piloted jet methane flames (Sandia F) with localised extinction, we obtain that at the experimentally determined blow-off velocity of the swirling spray flame, the predicted flame also blows off, demonstrating that the LES-CMC approach can capture the global extinction point in a realistic configuration.
Highlights
The extinction process is a strongly unsteady phenomenon and its experimental and numerical investigation is a very challenging task.A
The spark ignition of a heptane spray in a bluff-body configuration was examined experimentally in Ref. [1] and it was simulated numerically in Ref. [2] using the Reynolds Averaged Navier-Stokes (RANS) approach combined with the Conditional Moment Closure (CMC) combustion model [3]
The present paper aims to examine if Large Eddy Simulation (LES)-CMC can predict localised extinction for spray recirculating flames and, more importantly, if the global blow-off condition can be predicted
Summary
The extinction (or blow-off) process is a strongly unsteady phenomenon and its experimental and numerical investigation is a very challenging task. An experimental analysis of spark ignition and blow-off processes of an n-heptane spray flame in a bluff-body swirl burner was done [12,13,14] and the corresponding LES-CMC of spark ignition [15] showed that the LES-CMC can capture the spatial distribution of the ignition probability. Both experiment and LES have shown a very rich and variable behaviour of the flame following spark ignition and, to a large extent, ignition probability becoming lower than unity has been attributed to localised quenching, a physical phenomenon that lies at the heart of the global blow-off of flames. To the authors’ knowledge, this study constitutes one of the first efforts to predict global blow-off with combustion LES
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